The term "spandex" is employed in the art to describe a long chain synthetic fiber comprised of at least 85% by weight of a segmented polyurethane. The segmented polyurethane is composed of soft segments and hard segments. The soft segments can be polyether-based portions of the polymer chain, such as are derived e.g. from poly(tetramethylene ether)glycol. The hard segments can be derived from the reaction of an organic diisocyante, such as methylene-bis-(4-phenylisocyanate) with a diamine chain extender.
Spandex fiber has long been known in the art to impart desirable elasticity to textile goods. In many uses, spandex fibers are employed in combination with other textile fibers, notably nylon 6,6, in order to achieve some particular combination of aesthetic, comfort, and economic goals. Such combinations are achieved by combining fibers of spandex with fibers of nylon 6,6 during the textile fabrication process. One particular textile end-use is in pantyhose. Unlike many textile goods, pantyhose have very limited lifetime, and are discarded frequently, creating a significant waste stream. Until the development of the present invention there was no means for recycling that waste stream in an economical way.
While chemical separation of the spandex from the nylon was known, it was not cost-effective. Clearly the best approach was to shred the pantyhose and melt extrude the polymer into pellets or new fibers. However, spandex polymer exhibits considerable degradation when extruded at the temperatures of ca. 265.degree. C. or greater normally required for extrusion of nylon 6,6.
Michels et al., GDR 105974, disclose a process for extruding polymer melts consisting of two or more components which do not react chemically with one another and do not form a microscopically homogeneous solution. However, only blends of polyethylene terephthalate and polyethylene are disclosed. Extrusion temperature was 270.degree. C.
Franke et al., Angew. Makromol. Chem. 206, 21ff(1993), disclose the extrusion of blends of polyamide 6 with thermoplastic polyurethanes comprising at least 78% of thermoplastic polyurethanes. Extrusion was accomplished using a twin screw extruder with a melt temperature of ca. 230.degree. C.